Stupid 'new' math question - am I right or wrong here?

[Jeeebus]

So our son is in 1st grade and they are learning multiplication. The way they are teaching it is really bothering me. Either they are retarded or my whole life has been a lie. ATOT decides.

Ok so the problem is:

5 x 3

The way the textbook describes this is "5 groups of three" so 3 + 3 + 3 + 3 + 3

As opposed to the way I read the problem which is "3 groups of five" or 5 + 5 + 5

Yes, they should just teach multiplication tables and automatically know the answer, but that's a different rant.

The textbook interpretation of 5 x 3 doesn't make any sense to me and seems contrary to the English language.

So ATOT - am I right or is the school right?

 

[Ken g6]

Multiplication is commutative. You're both right.

Edit: While we're talking "New Math"...

 

[akenbennu]

Multiplication is commutative. You're both right.

This

 

[DeathReborn]

Technically 5+5+5 is the right method but both methods end the same. Just try not to confuse your kid too much.

 

[Hacp]

Multiplication is a mathematical function has the commutitive property. This means

a * b = b * a

Some functions do not have this property. Exponential functions are one example.

a^b != b^a

So you can say that it does not matter what the textbook says since both interpretations are equal.

 

[Anubis]

neither is wrong its just how you read it

five groups of 3: 3+3+3+3+3

5, 3 times: 5+5+5

 

[emperus]

So our son is in 1st grade and they are learning multiplication. The way they are teaching it is really bothering me. Either they are retarded or my whole life has been a lie. ATOT decides.

Ok so the problem is:

5 x 3

The way the textbook describes this is "5 groups of three" so 3 + 3 + 3 + 3 + 3

As opposed to the way I read the problem which is "3 groups of five" or 5 + 5 + 5

Yes, they should just teach multiplication tables and automatically know the answer, but that's a different rant.

The textbook interpretation of 5 x 3 doesn't make any sense to me and seems contrary to the English language.

So ATOT - am I right or is the school right?

It may be an error in the textbook. 5x3 should be read 5+5+5, but as everyone mentioned multiplication is commutative.

 

[dullard]

Like others have said, multiplication is commutative, thus both methods work.

But I disagree with this statement:

The textbook interpretation of 5 x 3 doesn't make any sense to me and seems contrary to the English language.

Do you say in English that you have 5 dozen eggs (5 groups of 12)? Or do you say you have dozen times 5 eggs (12 groups of 5)? English tends to put the "grouped items" into the second part of the math.

• Think of five families each with triplets. How many children are triplets? 5 groups of triplets = 15 (5 x 3). Most people wouldn't think to say you have triplets times 5 (3 x 5).
• Four Score = 4 groups of 20 = 4 x 20.

 

[Jeeebus]

Yes... you obviously end up with the same result so it technically doesn't matter, but it seems asinine to teach them that 5 x 3 should not be read the same way you would say it in English... 5 times 3 or 5 + 5 + 5.

 

[Jeeebus]

Like others have said, multiplication is commutative, thus both methods work.

But I disagree with this statement:


Do you say in English that you have 5 dozen eggs (5 groups of 12)? Or do you say you have dozen times 5 eggs (12 groups of 5)? English tends to put the "grouped items" into the second part of the math.

Think of five families each with triplets. How many children are triplets? 5 groups of triplets = 15 (5 x 3). Most people wouldn't think to say you have triplets times 5 (3 x 5).

Your examples are not presented as mathematical problems.

A recipe calls for 5 tablespoons of flour.

You want to double the recipe.

Is that 5 tablespoons + 5 tablespoons

-or-

2 tablespoons + 2 tablespoons + 2 tablespoons + 2 tablespoons + 2 tablespoons

 

[Jaskalas]

5+5+5 is shorter, thus faster and superior.

 

[dullard]

Your examples are not presented as mathematical problems.

You have a set of 10 bowling pins. You now want to double it. How many pins do you now have? Do you say in English:

A) A set of bowling pins times two. (10 x 2)

B) Two sets of bowling pins. (2 x 10)

English tends to favor option (B).

So most people would take 2 * (whatever you are talking about). In your example, that would be 2 * (5 tablespoons) not (5 tablespoons) * 2. Thus, two groups of five = 5 tablespoons + 5 tablespoons.

 

[CraKaJaX]

Is there a reason why saying it in English actually matters? I don't have kids, but I do know that the common core ways are a disaster. How are the asking for an answer? Do they want something stupid, like in words or colors rather than just a number? Since the outcome is the same (as a number), I wouldn't let it bother you much unless they are saying you are wrong.

 

[Anubis]

Is there a reason why saying it in English actually matters? .

yes but only because English is horribly inconsistent with how things are done

 

[purbeast0]

instead of being a dolt why don't you teach your kid that both ways are correct and it doesn't matter how you say it in english?

 

[dullard]

I don't have kids, but I do know that the common core ways are a disaster.

The OP is from Florida, which if I Googled correctly doesn't use the common core. So how is your post even remotely relevant?

 

[Anubis]

The OP is from Florida, which if I Googled correctly doesn't use the common core. So how is your post even remotely relevant?

Florida doesn't need common core, they are already at that level - see "Florida Man"

 

[IronWing]

A. Fives, we have three of them.

B. We have five threes.

B flows better but A is clearer in meaning.

 

[edro]

Show him both visual representations.
That way he won't be confused like you when he teaches his kid in 30 years.

 

[akugami]

As everyone has said, both are right.

5x3=15

I have 5 bags of balls. Each bag of balls has 3 balls in it. How many balls do I have?
3 + 3 + 3 + 3 + 3 =

I have 3 bags of balls. Each bag of balls as 5 balls in it. How many balls do I have?
5 + 5 + 5 =

Both problems, you can get 5x3 to get the answer but they're obviously different. And it's actually good for the teacher to present both.

 

[Muse]

Jees, man, I'm a math grad and to me they appear to be the same thing. Do you breath air or is the air breathed by you? Same thing.

 

[CraKaJaX]

The OP is from Florida, which if I Googled correctly doesn't use the common core. So how is your post even remotely relevant?

Pardon me while I post about apples and staplers and other irrelevant things in this thread.

 

[Jeeebus]

Do you breath air or is the air breathed by you? Same thing.

Actually you "breathe" air. "Breath" is air that is expelled during breathing.

 

[dullard]

Pardon me while I post about apples and staplers and other irrelevant things in this thread.

Did you have anything meaningful to post? Is there something specifically wrong with common core that you want to discuss, or are you just bashing it since it is the political hot-topic of last year? It sounded far more like you were a political hack (attacking the Republican's Common Core idea, even though the Republicans are now against it because Obama was for it) rather than actually contributing.

 

[Humpy]

....seems contrary to the English language.

Using English (probably other languages as well) to work a math problem confuses the hell out of people. It's difficult for many to accept that words do not have the same rigid meaning as mathematical symbols.